The invention relates generally to gas turbine combustion systems and more particularly to a technique for increasing flame-holding resistance, and enhancing fuel air mixing of a combustion system premixer.
Premixed combustion of natural gas or fuel oil has been commercially proven to be a highly effective means of minimizing NOx emissions for land based gas turbines. Similarly, partial premixing is commonly applied to achieve analogous emission reduction in aircraft engines. This mode of combustion introduces a risk of premature combustion or flame-holding when this premixed air-fuel flow ignites upstream of the intended combustion region. If the upstream region is not designed to sustain the high temperatures associated with combustion, overheating of components and subsequent hardware distress can occur. Increasing the premixing capabilities of a fuel-oxidizer is known to also increase potential combustion dynamics issues that may cause hardware damage.
One technique that has been employed to increase premixing capabilities of a fuel/air premixer makes use of an array of air passages. Another technique employs the use of premixing vanes to provide a swirl-stabilized premixer. Yet another technique that has been employed to increase premixing capabilities of a fuel/air premixer includes cratered fuel injection holes that additionally increase resistance to flame-holding.
These known premixer techniques, although offering advancements in mixing capability or resistance to premixer flame-holding, leave room for improvements to further optimize mixing capabilities and flame-holding margins for combustion system premixers. One modern mixing technique employs trailing edge features for both, signature and noise reduction, e.g. jet noise from aircraft engines. Such trailing edge features have not been investigated as a technique to enhance fuel/air premixing and resistance to premixer flame-holding within a combustion system premixer.
In view of the foregoing, it would be advantageous to provide an air/fuel premixing structure that preserves or increases the air/fuel mixing capabilities of known combustion system premixer structures associated with all types of gas turbine combustors, while providing increased margins to flame-holding. The air/fuel premixer structure should advantageously employ passive techniques to preserve or increase air/fuel mixing capabilities and increase resistance to flame-holding, while optionally minimizing regions of momentum deficit within the premixer.